It is not necessary to say much about the importance of the protectionagainst loss of useful genes under the influence of tree breeding programs andintensive forest management. Breeding always involves selection which resultsin the loss of some genes. By selection, we intend, of course, to retain favorablegenes and to discard unfavorable ones, but it is inevitable that many usefulbut still unknown genes may be lost in the process. Favorable genes are alsolost through the negative selection which is rather commonly practiced incommercial forestry. It is, therefore, urgently needed that some action be takento prevent the extinction of the hidden genes and to keep the gene pool largeenough for future improvements.

There are two ways to obtain this goal: one is the conservation of maturestands, either natural or artificial, and the other is establishing special newstands for the preservation of a broad gene pool.

The first could be said to be a static method. It does not require anyactual operation other than preserving nice stands in virgin forests or excellentplantations. Each reserve stand should desirably be made up of more than tenthousand individuals, which must be excluded from commercial utilization.Because of the large numbers of trees needed, there is considerable oppositionagainst such reservation, and it is very difficult to designate such stands solelyfor use in forest genetics. Therefore, any stand reserves must be connectedwith natural protection promoted from the view point of public health,recreation, protection of wild life and natural monuments.

The second method involving establishment of special stands is a dynamicone. Here, there is no need to reserve stands from a commercial forest, butit is only necessary to collect seeds from superior stands and to establish newstands from these. The newly established stands can then be commerciallyutilized when they become mature after the next generation has been establishedfrom their seeds. It is not difficult, therefore, to get support of the commercialforest management organizations for this approach.

In a population for which the gene pool is to be preserved, seeds mustbe collected in a rich seed year on scattered seed trees. There should be forty,fifty or more such trees, each better than average in vigor and quality. Treesnot selected as seed trees contribute their genes to the next generation throughtheir pollen. Selecting this many mother trees in every generation shouldinvolve little risk of inbreeding in later generations (Stern , 1959). If the

mother trees were well scattered throughout the population, but not scatteredtoo sparsely, we could then transfer nearly completely the gene pool of thepopulation into the seed lot.

The new platnations should include a large number of individuals. Sincesome of the useful genes may show very low frequencies such as 10~2 per centor less, it is evident that a large number of individuals is desirable. But theproductivity of such stands are not as large as those of the stands establishedwith the seeds of elite seed orchards, because the former have not passedthrough selections as intensive as the latter. Therefore, the establishment oftoo large plantations of such purpose is not desirable from the viewpoint ofcommercial forestry. Ten to twenty hectares must be the maximum on whichseveral ten thousand individuals can be grown. The plantations should bedivided into two or three plots and be located apart from each other, to avoidtotal destruction by accidents.

Individual plots should be no smaller than two or three hectares. If thepreservation of specific genes is the objective in the plantation, smaller sizeplots may be acceptable, but, on the other hand, the conservation of the totalgene pool requires larger plots because the peripheral members of the standscannot be used as seed trees for the next generation because of contaminationfrom foreign pollen.

In Kyusyu, the south-western most major island of Japan, we have beenmaking efforts to establish gene preservation stands since 1958. The efforts havebeen concentrated on the four main conifers, Cryptomeria japonica, Chamaecyparisobtusa, Pinus thunbergii and Pinus densiflora, which constitute the bulkof all plantations in this area. Cryptomeria and Chamaecyparis are not naturallydistributed in Kyusyu, with rare exceptions. Populations were selected, suchas (1) ones exhibiting very good performance, (2) fairly old plantations, (3)plantations famous for some special characteristic, and (4) undisturbed naturalstands. As for the two pines, on the other hand, there are many natural standsand naturally regenerated second growth, so the effort was concentrated innatural populations of nice growth and gcod tree from. However, nice plantationswere also sampled as well.

Seeds have been harvested from six stands of Cryptomeria, two ofChamaecyparis, five of P. thunbergii and two of P. densiflora. These seedswere sown in the nursery of Kyusyu Forest Tree Breeding Station at Kumamoto.The seedlings were divided into two lots for each population, one being sentback to the original Forest Districts and the second to some other Districts.They were planted by the State Forest agents in a manner similar to usualcommercial plantations. Unfortunately, the total area for each population hasbeen too small, five to eight hectares. Sometimes, mistakes occurred, forinstance, when two lots of seedlings of different origin were sent to one District,they were planted together in the same plot, making it impossible to get secondgeneration seeds of the characteristic gene pool for the two populationsseparately. These plantings are not yet enough for Kyusyu and must beexpanded. In the other parts of Japan, similar work has been started morerecently.

The »gene pool« plantations are registered and their development is observedperiodically. The stands will be harvested when they have reachedcommercial maturity. The time for collecting second generation seeds needsspecial considerations. In general, young stands do not supply suitable seed,

because (1) the performances expected at older ages are still not known, (2)inferior individuals have not yet been rogued and they contribute inferiorgenes to the population. However, in the case of gene preservation plantations,these points do not apply. Here the objective is to collect seeds from theregistered plantations with the minimum loss of genes. Therefore, the seedsshould be collected as soon as the stands reach full sexual maturity.

Besides the four major conifers, we have several tree species which areharvested in natural forests and are desired in the market but are not planted.Some of them supply rather large quantities of timber, such as Abies firma,Tsuga sieboldii, Castanopsis cuspidata, and Machilus thunbergii. Others, suchas Sciadopitis verticillata, Torreya nucifera, Betula grossa, Quercus gilva,Zelkova serrata, Cercidiphyllum japonicum, Cinnamomum camphora, andFraxinus sieboldiana, are rather scarce but produce timber of good quality.Natural stands usually show much smaller increments of standing crops thanartificial plantations, so they are being rapidly replaced with the latter.Although there are still fairly large stands of naturally regenerated secondgrowth, it is quite seldom that superior specimens of these species are ableto establish their offspring. Because of this, the preservation of the gene poolis urgently needed. In fact, it is already too late for some species such asT°rreya nucifera, of which almost all of larger specimen has been felledselectively.

For those species such as Abies firma or Castanopsis cuspidata which appearmore commonly in the form of almost pure stand, the same method ofsampling as for planted stands can be employed. For the species of rareoccurrence, it is necessary to select a sufficient number of seed trees throughouta wider region in order to avoid considerable inbreeding.

It is well known that an isolated group of a few individuals have a highdegree of inbreeding, which increases generation by generation, until littlegenetic variation is shown within the group (Sewall Wright efect). In suchcases, only a small area is needed for the preservation of each small population,but the desirable procedure is to obtain wide genetic variation by mixingseveral populations into a single plantation.

The species which are not often planted are usually slow-growers andrequire large dimensions for their commercial maturity. Therefore, they haveto be retained far longer than the usually planted conifers.Such slow growthis the main reason why these valuable species have not been artificiallypropagated, and it makes it difficult, at the same time, to get an area of forestland to plant the seedlings for gene preservation. In the authors opinion, thebest place to grow them is on the protection belts which separate commercialplantations and consist of natural vegetations. The belt is used as a safeguardof the plantation against fire or pests and, in total, amounts to very largeareas. It is, therefore, favorable not only from the genetic point of view butalso from the commercial one that the seedlings of these valuable species areplanted mixed with natural second growth, because the operation will giveincreased quality products.

Unfortunately, we have not yet been able to start such a program, butthere are good prospects to do so soon.

Finally, we have to discuss the analysis of the genetic variation of thepopulations. From the view point of gene preservation only, it is not necessaryto distinguish seeds from individual seed trees, but it is not difficult to collect

and sow the seeds separately. It has been proven that these single tree progeniesare very valuable as the materials for studying the genetic nature of populations.Therefore, the author wishes to recommend the parallel establishment ofprogeny trial for each population, so that the information about the geneticnature of the population will be available along with the major function ofacting as a gene pool. However, for the purpose of simplifying the work, manyof our early plantations were not accompanied by such progeny trials.

The author wishes to express his thanks to Professor Bruce Zobel whohas kindly read and corrected the manuscript.